In healthy dogs, the pulmonary artery carries blood to the lungs to be oxygenated, then goes back to the heart to get pumped out to the body via the aorta. In the fetal stage, all dogs have what is called the ductus arteriosus (DA) – a connection between the aortic arch and pulmonary artery. This vascular connection causes the majority of the blood in the right ventricle to bypass the non-working and fluid-filled lungs, and go straight to the aorta. Because the blood going into the neonate’s heart is already oxygen rich from the mother’s heart, it has no need to pick up oxygen in the pup’s lungs. In fact, if the DA closes before the pup is born, the right ventricle can become damaged if it pumps against the resistance in the lungs.
Once the dog takes a few breaths after birth, the ductus arteriosus begins to narrow. In healthy dogs, the connection is closed after a couple of days. In some pups, that channel fails to close. This condition, called patent ductus arteriosus (PDA), reduces the amount of blood that travels through the pulmonary artery to the lungs, which reduces the amount of oxygenated blood that eventually gets delivered to the body. In addition, PDA increases the burdens placed on the left chambers of the dog’s heart. This leads to dilated or enlarged chambers, and eventually, congestive heart failure and death.
This is one of the most common heart defects in dogs, but very little is known about what causes it. PDA may be caused by one or more factors, including exposure to toxins, pharmaceuticals, infectious diseases, nutritional deficiencies, or environmental factors during development in the womb. Many vets consider patent ductus arteriosus to be an inherited disorder.
There is no known way to prevent PDA in dogs. Affected dogs should be removed from the breeding program. Dogs with siblings that develop the disorder should be examined and some breeders remove these unaffected dogs from the breeding program as well, in case there is a genetic factor that will pass to their pups.
Some dogs show no signs of PDA for years, but some dogs experience visible symptoms by the age of one year. Because this congenital defect is repairable by surgery, it is important that it is diagnosed as soon as possible to prevent heart failure or other damage that is irreversible. Talk to your vet immediately if you notice any of these symptoms: exercise intolerance, palpable heart murmur, failure to thrive, bounding pulse, fatigue, stunted growth, lethargy, weakness, respiratory distress, cough, collapse, and seizures.
Dogs at Risk
Females are more likely to develop PDA compared to males. Breeds predisposed to the disorder are the Pomeranian, Shetland Sheepdog, English Springer Spaniel, Yorkshire Terrier, German Shepherd, Maltese, Keeshond, Collie, Bichon Frise, Cavalier King Charles Spaniel, Cocker Spaniel, Labrador Retriever, Chihuahua, and the Poodle (Standard, Toy, and Miniature versions).
Testing and Diagnosis
Most cases are diagnosed during a dog’s first few visits to the vet for vaccinations and puppy wellness checkups. PDA causes a distinct heart murmur that varies in loudness depending on the phase of the heart cycle. The murmur is detectable through a stethoscope, and can be felt if the vet places a hand behind the pup or dog’s left elbow. On the hand, it feels like the churning of a washing machine.
The vet should take x-rays of the chest to look at the dog’s lung, heart, and vessel size and appearance. An ECG will identify any hypertrophy or dilation in the chambers of the heart, and will show irregular heart rhythms. A blood sample will show anemia.
Further testing may include an echocardiogram to show the degree of contractility of the muscle, the size of the heart chambers, and the thickness of the heart chamber walls. Some echo tests can even determine how fast the blood flows through the PDA, and how much pressure is placed on the different chambers of the heart.
Treatment and Prognosis
Patent ductus arteriosus is highly treatable – in fact, it is surgically correctable with no ill effects if it is caught soon enough.
Depending on the vet’s expertise, the surgery to correct PDA may be done in a regular vet clinic. Otherwise, the dog may receive a referral to a veterinarian cardiologist. The surgery is called ductus ligation. This involves general anesthesia, which involves the risks typical to any surgery. The vet enters the chest cavity and ties off the PDA.
In older dogs that have progressed to congestive heart failure before the disorder is diagnosed, surgery can have increased risks, but these risks can be lessened with the use of vasodilators, diuretics, and enforced rest.
Once the dog has made it through a few weeks of physical restriction to allow recovery, it will usually be capable of returning to its pre-surgery activity level. During recovery, all dogs should get a lot of rest and avoid stressful situations.
Most dogs have a very good prognosis once the surgery is complete. They will often experience an improvement in the quality of life and will go on to live long, healthy lives. Dogs with untreated PDA have a grave prognosis – they eventually will develop congestive heart failure and die.